The 2011 ASHS Annual Conference

Greenhouse experiments were conducted in the summer of 2010 at Texas Tech University to evaluate the response of Oenothera elata transplants to postemergence herbicides. Plugs (3.5 cm in diameter) were transplanted into 11.3 liter pots filled with a Brownfield sandy clay loam (loamy, mixed, superactive, thermic Arenic Aridic Paleustalfs) with a pH of 8.0 and organic matter content of 1.2%. Fertilizer (14N-14P₂O₅-14K₂O) was applied at time of transplant at a rate of 24 kg N/ha. Irrigation was applied through an automated system throughout the study to ensure optimal growth and prevent wilt stress. Pots were maintained weed free by hand weeding in order to eliminate plant competition. Eight herbicide treatments and a non-treated control were examined. Treatments were applied using a CO₂ backpack sprayer equipped with XR8004VS nozzle tips and calibrated to deliver 375 L/ha at 221 kPa. Postemergence herbicide treatments were applied 21 days after transplant and consisted of glyphosate at 1.68 kg ai/ha, quinclorac + mecoprop + dicamba at 0.69 kg ae/ha, glufosinate at 0.84 kg ai/ha, fenoxaprop at 0.1 kg ai/ha, fluazifop at 0.45 kg ai/ha, mesotrione at 0.21 kg ai/ha, sulfosulfuron at 0.06 kg ai/ha, and quinclorac at 0.42 kg ae/ha. The trial was arranged in a randomized complete block design with 5 replications of treatments. Percent phytotoxicity was assessed visually 3, 5, 7, 14, 21, and 28 days after treatment (DAT) using a scale of 0 (no phytotoxicity) to 100% (plant death). 0. elata plants were harvested 28 DAT, separated into above and belowground biomass, dried, and weighed. Data were subjected to analysis of variance and means were separated using Fisher’s Protected LSD at the 0.05 significance level. All treatments, except fluazifop (5%), exhibited 26 to 49% phytotoxicity 7 DAT. Glyphosate and fluazifop exhibited 4 and 22% phytotoxicity, respectively, 28 DAT. All other treatments exhibited ≥ 50% phytotoxicity 28 DAT. All treatments, except fluazifop, exhibited significant reductions in shoot weight (62 to 91%) compared to the non-treated check 28 DAT. All treatments, except fluazifop, exhibited significant reductions in root weight (72 to 96%) compared to the non-treated check 28 DAT.